API: RMA requires a valid connection on both sides

CCI's disconnect is a local operation. The peer is not notified.
If the peer holds a formerly valid RMA handle and attempts to use
it after the local side has called disconnect, the RMA should fail
with CCI_ERR_DISCONNECTED.
Merge pull request #33 from CCI/topic/disconnected-rma

API: RMA requires a valid connection on both sides